In windows, I used to use a text editor called crimson editor which featured the best column-mode editing support I have yet to use.

When enabled via a simple Alt-C shortcut, selections could be made with the mouse or cursor keys and they would be visual blocks rather than wrapped-lines.

These selections could be deleted, moved, copied, pasted, and all of the operations just made sense. You could also just start typing, and you'd get a column of the characters as you're typing.

There are multiple ways of getting parts of the these features working separately discussed on this forum thread, but no one has yet to provide a solution that provides this all-encompassing and easy-to-use method.

If someone could point me to a gedit plugin where this work is actively being pursued, perhaps I could help with the coding myself. If someone is aware of a text editor that already provides this full functionality, I'd appreciate the info. Running crimson editor through wine and the close-but-not-quite multi-edit plugin for gedit are the temporary solutions I'm 'getting by with' for the time being.

UPDATE (2012-11): I'm now a very happy user of sublime text. It supports excellent column-mode editing and works on all three major OS platforms without any issue. Highly recommended!

If you are familiar with emacs, emacs provides column editing support via many modes but requires getting used to (aka learning curve). I can detail if it will answer your question.
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koushikOct 12 '10 at 15:03

To edit columns, I use vi / gvim. This will take a bit of learning to get used to vi, but in the end many people find this to be their preferred editor.

Specifically within vi you can use CTRL-V to highlight columns in visual mode, then you can edit it as you would expect. I use this all the time for adding and removing comments, or indenting functions ie CTRL-V (highlight a column) SHIFT-I '#' ESC will comment out that entire column.

Old school (Motif) but has tabs and is lightweight and simple. Has context highlighting included for a number of coding languages, and more can be added.
Pressing Ctrl while dragging with the mouse enables a block of text to be selected.
Then you can copy/paste as usual. Couldn't do without this feature now.

The emacs column mode features are really cool. They go far beyond just copy/paste of rectangular text. Check out the video for a demo of how to simultaneously edit all the lines in the column! Very handy!

If you don't want to watch the video (or can't) here are the bare basics:

CUA-mode's superior rectangle support is based on using a true visual representation of the selected rectangle. To start a rectangle, use [S-return] and extend it using the normal movement keys (up, down, left, right, home, end, C-home, C-end). Once the rectangle has the desired size, you can cut or copy it using C-x and C-c, and you can subsequently insert it - as a rectangle - using C-v. So the only new command you need to know to work with CUA-mode rectangles is S-return!

On Kubuntu 12.04 and emacs v24, [S-return] is CONTROL-RETURN (CTRL-ENTER) for me.

As already mentioned, Scite has this built-in (no plug-ins needed). It's very easy to use. And Scite is in the Ubuntu repos.

Rectangular blocks of text can be selected in SciTE by holding down the Alt key on Windows or the Ctrl key on GTK+ while dragging the mouse over the text.